Abstract
Abstract. The outflow of supercooled Ice Shelf Water from the conjoined Ross and McMurdo ice shelf cavity augments fast ice thickness and forms a thick sub-ice platelet layer in McMurdo Sound. Here, we investigate whether the CryoSat-2 satellite radar altimeter can consistently detect the higher freeboard caused by the thicker fast ice combined with the buoyant forcing of a sub-ice platelet layer beneath. Freeboards obtained from CryoSat-2 were compared with 4 years of drill-hole-measured sea ice freeboard, snow depth, and sea ice and sub-ice platelet layer thicknesses in McMurdo Sound in November 2011, 2013, 2017 and 2018. The spatial distribution of higher CryoSat-2 freeboard concurred with the distributions of thicker ice-shelf-influenced fast ice and the sub-ice platelet layer. The mean CryoSat-2 freeboard was 0.07–0.09 m higher over the main path of supercooled Ice Shelf Water outflow, in the centre of the sound, relative to the west and east. In this central region, the mean CryoSat-2-derived ice thickness was 35 % larger than the mean drill-hole-measured fast ice thickness. We attribute this overestimate in satellite-altimeter-obtained ice thickness to the additional buoyant forcing of the sub-ice platelet layer which had a mean thickness of 3.90 m in the centre. We demonstrate the capability of CryoSat-2 to detect higher Ice Shelf Water-influenced fast ice freeboard in McMurdo Sound. Further development of this method could provide a tool to identify regions of ice-shelf-influenced fast ice elsewhere on the Antarctic coastline with adequate information on the snow layer.
Highlights
Ice shelves are the floating extension of the grounded Antarctic ice sheet and buttress the flow of the grounded ice streams (Fürst et al, 2016)
The outflow of supercooled Ice Shelf Water (ISW) from the conjoined McMurdo–Ross Ice Shelf cavity results in a consistent pattern of thicker fast ice with a substantial sub-ice platelet layer (SPL) in the central-western region of McMurdo Sound
CryoSat-2 ice freeboard was obtained from surface elevation measurements by applying a supervised retrieval procedure which manually identified the relative sea surface height along the track in satellite imagery
Summary
Ice shelves are the floating extension of the grounded Antarctic ice sheet and buttress the flow of the grounded ice streams (Fürst et al, 2016). Ice shelves and outlet glaciers comprise 74 % of the Antarctic coastline (Bindschadler et al, 2011), presenting an enormous interface where the ocean can directly interact with the grounded ice sheet. When fast ice attaches to ice shelves or outlet glaciers it forms an important interface between the ice sheet and open ocean/pack ice (Giles et al, 2008; Massom et al, 2018). Fast ice affects ice sheet mass balance by providing mechanical stability and by buttressing glacier tongues (Massom et al, 2010) and ice shelves from the impacts of ocean swell (Massom et al, 2018)
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